Positive column lamp



0a. 22, 1935. L. BECK I 2,018,620,

POS ITIVE COLUMN LAMP Original Filed May 31, 1932 9 INVENTOR M-ULBEC/fBY ATTORNEYJ Patented Oct. 22, 1935 PATENT OFFICE POSITIVE COLUMN LAMPLeo L. Beck, Westfield, N. J., assignor to Claude Neon Lights, Inc., NewYork, N. Y., a corporation of New York Application May 31, 1932, SerialNo. 614.403 Renewed March 16, 1935 6 Claims.

The present invention relates to gas discharge positive column luminoustubes.

It is a continuation in. part of applications Ser. No. 373,922 filedJune 26, 1929 and Ser. No. 432,024 filed February 28, 1930.

The luminous rare gas tube signs now commonly employed for display andadvertising purposes have largely displaced the older electric signsemploying incandescent bulbs. Nevertheless such tubes are subject tolimitations that have greatly restricted their sphere of usefulness. Thevoltage necessary to operate such tubes is high, e. g. 2,000 to 20,000volts. At such high voltages only very small currents can be used.Consequently, the brilliancy of such tubes,

i. e., the light energy emitted per unit area of the tube surface, isvery low, so low that the daylight advertising value is poor. By this ismeant the fact that such tubes are relatively inconspicuous in sunlightor daylight. Darkness is required to make such tubes effectiveand'therefore they possess their chief. attracting value only at nightor on dark days or in dark places.

Moreover, for general illuminating purposes, such tubes have not provensuccessful owing to a large extent to the fact that it is difficult toconcentrate the light thereof in to a small space, that is, on accountof the small amount of light energy emitted per unit area of tubesurface, it is extremely diff cult to concentrate into a convenientvolume enough energy to render such tubes available for generalilluminating purposes, e. g., the illumination of oillces, factories,homes, etc.

The present invention marks a long step for ward in the luminous tubeart.

It provides a luminous tube which can be operated at ordinary supply orline potential of the order of 110-220 volts, and at high currentdensities for example 0.1 to 1.25 amperes per square centimeter ofpositive colunm cross section.

It provides a luminous tube having a high.

brilliancy, for example a brilliancy of the order of 1.5 Lamberts. (TheLambert is a practical unit of intensity and is edual to one lumenemitted per square centimeter of. the diffusing surface.) Thisbrilliancy is many times greater than that characterizing the oldertubes and as a result, the advertising value of the tubes of the apresent invention is about as much greater than that of the older tubesas that of those tubes was, in turn, greater than the advertising valueof the incandescent bulbs which were largely replaced by the former.

It provides a luminous tube by m ans of which a large quantity of lightmay be concentrated into a relatively small space. For example, in theolder tubes, taking as an example a length of tubing about 3 feet longand millimeters in diameter, it was customary to have a current of 5about 0.030 ampere at a potential fall of about 300 volts in a fillingof neon gas, said gas having a potential drop of about 100 volts perfoot. The energy consumed was therefore about 300x .030: 9 watts. Thepotential fall of a tube of the present invention having the samediameter may be only about 100 volts, but the current may be as much as0.5 ampere or more, with a corresponding energy consumption of 50 ormore watts. The amount of light emitted is roughly proportional to theenergy input and therefore the light of the present invention is muchmore intense than that of the older tubes. Consequently, it is availablefor general illuminatingpurposes, indoors and outdoors, and is notrestricted to the field of advertising and display. In fact, the presentinvention inaugurates a new era in illumination. I

One of the problems solved by the present invention was the problem ofilluminating a considerable length of tubing when only a low potentialof 110-220 volts was available. With the older tubes which operated atextremely high voltages this problem was not presented and it wascustomary to operate lengths of tubing as much as ten feet in length.The details of the solution of the problem will be more fully describedhereinafter, but it may be said that the solution of the problem openedthe door to the solution of the problem of increasing efliciency ingeneral, that is, the success achieved in operating considerable lengthsof tubing at low voltage turned out to be only one phase of the problemof increasing efliciency so that whether the length of tubing be shortor long, it may, according to the present invention, be operated at agreatly improved efllciency. For the preparation of many types of tubingfor sign and display purposes, it is necessary that a certain minimumlength of tubing be successfully illuminated, this for the reason thatsuch tubing has to be bent into various shapes and for the bendingoperation there is always a certain minimum length that cannot bereduced. The present invention provides a tube long enough to be bentinto the shape of a letter or other desired design, even thoughthe-available voltage may be as low as 110 volts. In other. words, thelength of tubing or what amounts to the same thing, the "quantity oflight obtainablefrom a source of predetermined potential has beengreatly increased. The invention, having increased eiliciency on longtubes, is however applicable toa tube irrespective of the length.

The overall efllciency 01- a tube or lamp or the present invention maybe as high as 18 lumens per watt electrical energy consumed. Moreover,such light may be substantially of one color, for example thecharacteristic orange red color of neon. The possibility of obtaining somuch light of a given color from a unit quantity oi electrical energy,i. e., the "color efllciency",is incomparably, greater than thatobtainable with the older incandescent lamps.

- tures thereof to obtain light having a wide range oi colorcharacteristics and by a suitable blending, light having substantiallythe same composition as daylight may be produced. Thus-the interior orexterior of buildings may be illuminated either by artificial daylightor by light having any desired color. The decorative and utilitarianpossibilities of the lamps of the present invention are almost infinite.

The present invention relates particularly to tubes employing neon asthe principal gas filling,

in which the source of light is that radiated by a positive column of.the rare gas. Such lamps are distinguished from those in which the lightemanates largely from a film or luminous gas cover-v ing a cold cathode,known as negative glow lamps.

In lamps of this class, the electrodes are so close together that nopositive column exists. The

luminosity of such lamps is very low and the source of light is verydifferent from that radiated by the positive column light of the presentinvention. In negative glow lamps most of the potential fall occurs atthe cathode, resulting in great inemciency, whereas in the lamps of thepresent invention by far the greatest potential drop occurs through therelatively long column of gas which constitutes the positive column, the

cathode drop being a very minoriraction o! the overall voltage.

. The group of rare gases, argon, krypton and xenon have collectivelyand individually a much lower potential gradient than neon. Thepotential gradient is a measure of the resistance of the gas to thedischarge or electricity through it by ionization and may be expressedas the minimum potential fall or drop, which occurs through a unitcolumn of gas, 1. e., a unit length of gas column in a tube having agiven diameter, when that column or gas is ionized and illuminated by anelectrical discharge. 1

I have found that the potential drop through a positive column of neoncan be greatly decreased by incorporating with the neon smallproportions, e. g., 0.05 to 1.0 per cent of a gas selected from thegroup composed of argon,krypton and xenon. For example I haveincorporated with neon, in a tube having a length of about forty inchesbetween the electrodes, and an inside diameter of about 14.5 millimetersand provided with a thermionic cathode, about-0.5 per cent-oi argon, andhave found that the potential drop between the cathode and anodeis'greatly educed.- This discovery is a considerable advance in the artbecause it permits a much longer tube to be operated from a source ofcurrent of fixed or predetermined potential. I found, however, that theluminosity oi the positive column or neon tends to be decreased by theincorporation 5 of the low potential gradient gas, whether the latterbeargon, krypton or xenon, that is, the characteristic orange red neoncolor tends to be impaired. However, I then discovered that, withoutsacrificing the potential-reducing property of the low potential gas, Icould restore the brilliant intense neon color by increasing the currentdensity. This result was unexpected but very gratifying because by thecombination of increased current density and use of argon, krypton orxenon (in conjunction with a principal filling or neon) I was able toobtain a high lumi nosity oi neon at a greatly increased efliciency,that is, at a greatly decreased potential drop or gradient through thecolumn of mixed gases.

This new result was quite unexpected because it was thought that byincreasing the current density I would merely increase or accentuate thepale, insipid light radiated by the argon, krypton or xenon. Insteadhowever. upon reaching a certain minimum current density, the neonsuddenly shone forth in all its brilliance.

By experiment I round that a relation exists between the per cent of lowpotential gradient gas and the minimum current density necessary to usein order to offset the dimming effect of the low potential gradientgasand restore the brilliant neon light; or to put it another way,

a relation exists between the current density and the maximumpermissible percent 01' low potential gradient gas, (i. e., argon,krypton or xenon). For example, taking argon as an example ot a lowpotential gradient gas, it the current density is about .0.1 ampere persquare centimeter 01' positive column cross section, then the maximumpermissible per cent of argon is about 0.1 per cent (the remainder beingneon). As the current density increases, more and. more I argon may beemployed, so that if a current density as high as 2.5 amperes per squarecentimeter of positive column cross section be employed, as much asabout 1.25 per cent of argon can be used, and as the proportion of argonis increased, the emciency oi the tube increases. For manypurposeshowever, it sufllces to use about 0.20 per cent of argon and a currentdensity of about 02 to 0.25 ampere per square centimeter of crosssection. With extremely high current densities such as 2.0 to 2.5amperes per square centimeter considerable energy is lost in the form ofheat so that it is generally desirable to .use just as little .lowpotential gradient gas as possible. Krypton is more efllcient than ar--gon, that is.'it requires much less krypton than argon to produce thesame increase in lighting efliciency. For example, about 0.15 per centof krypton will accomplish the same result'as about 0.30 per cent ofargon. v

I recommend for ordinary purposes, that is, 35 for ordinary illuminatinglamps and display tubes, a range of proportion of low potential gradientgas of 0.05 to 0.50 per cent and a corresponding range of currentdensity of 0.05 to 1.0 amperes per square centimeter of cross section ofthe positive column. Where it is necessary to have a higher currentdensity in order sity of the order of 2.5 amperes per square centimeterof positive column cross section.

In addition to providing the tube with a gas.

filling which operates at high efficiency, I also provide it withsuitable electrodes, one or both of which is a thermo-emissive orthermionic electrode depending on whether direct or alternating currentis used. I make the cathode sumciently emissive so that at the cathodethe fall of potential is very low as compared with cold cathodes. Thisis done by coating a metalLc grid with a suitable salt or oxide ofbarium (or a mixture of salts or oxides of barium and strontium) andthen activating the cathode i. e., heating the cathode, decomposing the.salt or oxide and bombarding the residual decomposition product todevelop oractivate the residue and render it capable of emittingelectrons when heated to a high temperature. When an electrode soconstructed acts as cathode, the oathode fall of potential is low andonly a small amount of energy is lost in the form of work ,done in thetransmission of energy from the emissive electrode .to the gaseous ions.Therefore the low cathode fall of potential coacts wiih the lowpotential drop through the positive column of gasto provide an overallor total potential fall through the tube which is lowenough to beoperable from a predetermined source of low voltage of the order of110-220 volts, even when a ballast resistance is in series with thetube.

The fall of potential through a column of rare gas in a tube is afunction of the diameter of the tube and pressure of the gas andaccording to the present invention the pressure of gas for a given gas,and for a tube of given diameter is so chosen that the pressure is anoptimum one, i. e., a pressure corresponding to a minimum potentialgradient. For example, if the tube has an inside diameter of about 15millimeters thepressure of gas is preferably about 7 'to 8 mini-'-meters and if the tube has an inside diameter of 30 millimeters theoptimum pressure is less, e. g., I to 3 millimeters from whichinformation it will be observed that the optimum pressure decreases asthe diameter of the tube increases.

The invention will be described in greater detail by reference to theaccompanying drawing which shows one of the many forms of luminous tubesthat may be employed to embody the manufacture of the present inventionand means for practicing the art or process thereof. v Figure 1 shows aluminous tube with thermion'ic cathodes and a diagrammaticrepresentation of the external electric circuits for operating the tube,parts being broken away to more clearly show the constructionof thetube.

Figure 2 is an enlarged section on the line 2--2 of Figure 1 showing aplan. view of the grid cathode.

Figure 3 shows a strip of metal used in the construction of the cathodeshown in Figures 1 and 2.;

Figure 3 shows a strip of metal l6 four inches in length and increasingin width from the ends toward the center thereof. The width of vthestrip at the ends is 2 millimeters and at the center is 3 /2millimeters. It is mad'e'of a nickel silicon alloy and has a thicknessof about 0.002 inch. This strip of metal is then bent and shaped intothe form of a grid, as shown clearly in Figure 2. The ends of this gridare then joined with supportingp'osts or wires II and connectedrespzciively with lead wires 2 and 5 for one electrode and 9 and ill forthe other electrode. Prior to asrembling the tube with its gridelectrodes, the latter are degasified by heating at a high temperaturein an atmosphere of hydrogen. They are then cooled, and coated with acoating comprising barium carbonate or other suitable substance and aresubsequently mounted in the tube and heated to a high temperature suchas 1000 C. or 1200 C. in vacuo. Decomposition of the coating takes placein the presence of the nickel silicon alloy and the latter becomescoated with a firmly adherent and highly emissive coating. Aft:rassembling the tube, evacuating it and activating the coating on theelectrodes by heating, and as hereinafter described, the tube is chargedwith a filling which in a typical case is a mixture of neon with about0.25 per cent of argcnat a pressure of 7 millimeters (at 25 C.). Theinside diameter of the tube in this typical case is 14.5 millimeters andthe distance between the electrodes is 40 inches. The discharge currentsupplied to the tube through the lead.

is a reatively high current density as compared' with currents of 25 to30 milliamperes employed in high voltage cold cathode tubes. Typicalrange; ofcurrent densities which may be employed are from 0.05 to 2.5amperes per square centimeter of cross section ot the gas columncorresponding to a range'of proportion of low a potentialgradient'gas-from 005 to 1.25 per cent.

As a guidein selecting the proper current density for a given per centof low potential gradient ga: the followingtable is submitted:

Percent Percent density neon argon l per centimeter) (Approximate) 99-90 0. l0 0. l 99. 75 0. 25 v O. 3 99. 0. 50 0. 9 99. 25 0. 75 1. 3 99.()0 l. 00 l. 8 98- 75 .1. 25 2. 4

of the cathode near the supporting wires l8 have a tendency to be coolerthan the other portions of the cathode with the result that the emissionat those points is lowered, and there is thus a tendency for emission tobe concentrated in the said other portions. It has, however, been foundpossible to compensate for this lack of uniformity by increasing thesurface of the cathode progressively towards the center portionsthereof, as shown clearly in Figures 1 and 3, and by this means it hasbeen found possible to provide a cathode having .an improved emissionfrom the print of view of uniformity and uniform distribution of theemission over the entire surface theremethod of accomplishing this is toemploy the ring members 32. Each of these is supported by a wire 34passing through the press andis in spaced relation to the correspondingelectrode, so that it is possible to pass a discharge current betweenthe electrode and its ring during manufacture of the C. is reached,exhaustion being; continued during the baking operation. By means ofcircuits not shown in the drawing a heavy current (e. g. 11.5

'amperes) is sent through each electrode to heat it by resistance anddecompose the coating there- .on, (which may be a mixture of thecarbonates of strontium and barium). when the vacuum gauge shows that nomore gas is evolved from the decomposition in this manner, the mode ofheating Just described is terminated and a direct discharge currentpassed between each cathode and its corresponding ring I! by connectingthe wires 34 to the positive pole of a source of current and theelectrodes l to'the negative pole and passing a discharge currentbetween the respective rihgs as anodes and the respective. grids i ascathodes. Ionization or are current now flows from ring to grid as shownby the appearance of a blue glow in the intervening space. v Pumpin iscontinued until the blue glow disappearaand the rings 32 become red hotdue tobombardment by electrons.

At this point, a' pure electron discharge occurs from cathodes i totheir corresponding activating rings or anodes I2 and the. vacuum in'thetube should be very high (e g. II- mm. of mercury) exhaustion havingbeen continued during the activation. The getter is now flashed, thetube is allowed to cool to room temperature and a mixture of neon with aproper proportion of low potential gradient gas is then introduced intothe envelope 8 whereupon the latter is sealed off from the pump (notshown in drawing).

These details of construction of the electrodes or their equivalents aredesirable to provide electrodes which will, during a period of usefulcommercial life, ully withstand the action of'currentsofhighdensityandatthesametime function-at a low cathode'drop.During operation of the tube when in commercial me, more or less tthereof by positive ions may ocour and the electrodes must stand up\mder this bombardment in order to be..The-inventionalsoincludesasapartofthe combination thereof an improvedelectrical circult for supplying heating current to the thermoemissivecathodeorelectrodesandforsupplying discharge current. .As shownin Figure L'the coils II and 22 receive current from acommonprimaryooilflandthiscurrentpasseathrough-theleadwireslandlandilandireespectivelyandthroughthegridsofthe'electrodes to heat the same to anemissivetemperature.

'Inthetypicalcaseieferredbabovethehuting current'necessary to securesatisfactory operationoftheelecirodesmaybelamperes'ineachoftheheatingcircuitsthesaid 'coilsllandll. Thedischargecurrentatmvoltsistappedoifatthepointsflandliandthe discharge circuit comprises aninductance II,

This inductance or its equivalent is included in the discharge'circuitasanelementthereofpartlytocausethecurrenttolagbehindthevoltlgesoastoobviatethetendenoyofthetubetobeexns i-sattheendofeachhalf-cycleandto P de for asteadrlight. Thesaid may consistof a coil wound upon a closed core and may be provided with anadjustable airgap so as to be variable. The inductance also acts as aballast or choke and acurrent limiting device. Wide ranges of currentdensity may be applied'to the 5 tube by adjusting the values of theinductance. As shown, the inductance, the secondary coil, and theprimary coils are enclosed in a box and there is thus provided a verysimple and emcient current supplying means for the discharge 10 tube inwhich are combined the means not only for supplying discharge currentbut also heating current for, the electrodes.

The rings 32 perform a very helpful function not only during manufactureof the tube but also l when it is in use commercially. After themanufacture of the tube is finished, the wires 34 are respectivelyjoined to the wires 6 and Ill and the rings 32 thus become a part of thedischarge circuit. During each half cycle of the discharge 2 whichoccurs with alternating current, through the circuit 3, 5, ".10, II, IIand I, the ring 32 at one end of the tube acts as anode while the grid lattheother end ofthe tube actsascathode. Thus; the ring carries theanode current and the grid carries the cathode current. It appears thatthe electron or anode current passes more easily from the gas to themetallic ring 32 than it would pass into the coated grid. In any event,the use of the ring in this way aids in preventing flickering and inincreasing the life of the cathode, whatever may be the theory toaccount for it.

' When it is desired to operate the tube, discharge potentialis appliedto terminals .3 and l. The current induced in coils 2. and 35 22 beatsthe respective electrodes I! at each end of the tube 8 to an emissivetemperature. Thereupon, ionizing means not shown in the drawing isapplied to the tube to'initiate the discharge. 8uch ionizing means maycomprise a high fre- 40 quency, field which is brought into proximity tothe tube so as to initiate ionization of thegas within the envelope l,orit may comprise an'inductive kick coil which may form a subsidiarypartof the dischargecircuitinsucha manner that the currentflowingthrough the said. coil issuddenlycollapsedtogenerateahighpotentialdischarge or kick in serieswith the-positive column between theelectrodes i. Other means of creating initial ionization of the gaswithinthe 'envelopemay also be employed and-as soon as.

such initial ionisationoccurs the'potentialappliedtotheelectrodesifromtheter'minalsland 4, causes the tube to"strike or become illuminated and thetubeofthepresentinventionthere-'after may be illuminated continuouslyorintermittentlythroughoutalongperiodofusefulcommerciallife.Itisalsotobeobservedthatthe.tubeshowninngurehinsteadofhavi'ngthestraight form of positive columntherein delineated may be bent'into any desired design according to theteachings of the present invention.

The'principles of the invention and certain illustrative embodimentsthereof have been completely described and disclosed herein and thisdescription and disclosure will enable all those centimeter of positivecolumn cross section, a gas selected from the group consisting of argon,krypton and xenon, the proportion of said gas being the maximum that canbe employed with respect to the current density without impairing thecharacteristic color of the neon, the range of this proportion beingfrom 0.05 to 1.25 per cent, and means to discharge through the tubecurrents having a density' of 0.05 to 2.50 amperes per square centimeterof positive column cross section.

2. A positive column gaseous discharge tube containing a principalfilling of neon, a thermionic cathode capable of transferring to the gasfilling electrical energy having a density of the order of 0.05 to 1.0ampere per square centimeter of positive column cross section, a gasselected from the group consisting of argon, krypton and xenon, theproportion of said gas being the maximum that can be employed withrespect to the current density without impairing the characteristiccolor of the neon, the range of this proportion being from 0.05 to 0.50per cent, and

means to discharge through the tube currents hkvinga density of 0.05 to1.0 amperes per square centimeter of positive column cross section.

3. The method of producing a positive column gaseous discharge light inanenvelope containing a principal filling of neon and a thermioniccathode capable of transferring to the gas filling electrical energyhaving a density of the order of 0.05 to 2.50 amperes per squarecentimeterof positive column cross section which comprises mounting thesaid cathode in the envelope,

charging the envelope with neon and a gas se-- lected from the groupconsisting of argon, krypton and xenon, the proportion of said gas beingthe maximum that can be employed with respect to the current densitywithout impairing the characteristic color of the neon, the range ofthis proportion being from 0.05 to 1.25 per cent, heating the thermioniccathode to an emissive temperature and discharging through the positivecolumn a current having a minimum density which is within the'range of0.05 to 2.50 amperes per square centimeter of cross section of thepositive column.

4. The method of producing a positive column gaseous discharge light inan envelopecontaining the principal filling of neon and a thermioniccathode capable of transferring to the gas filling electrical energyhaving a density of the order of 0.05 to 1.0 ampere per squarecentimeter of positive columncross section which comprises mountdensitywithout impairing the characteristic color of the neon, the range ofthis proportion being from 0.05 to 0.50 per cent, heating the thermioniccathode to an emissive temperature'lo and discharging through thepositive column a current having a minimum density which is within therange of 0.05 to 1.0 ampere per square centimeter of cross section ofthe positive column. 15 .5. A positive column gaseous discharge tubecontaining a principal filling of neon, a thermionic cathode capable oftransferring to the gas filling electrical energy having a density of vthe order of 0.10 to 1.0 ampere per square 20 centimeter of positivecolumn cross section, a gas selected from the group'consisting of argon,krypton and xenon, the proportion of said gas being the maximum that canbe employed with respect; to. the current density without impairing thecharacteristic color of the neon, the range of this proportion beingfrom 0.10 to 0.50 per cent, and means to discharge through the tubecurrents havinga density of 0.10 to 1.0 ampere per square centimeter ofpositive column cross section.

6. Themethod of producing a positive column gaseous discharge light inanenvelope containing a principal fillirg of neon and a thermioniccathode capable-of transferring to the gas filling electrical energyhaving a density of the order 3 of 0.10 to 1.0 ampere per squarecentimeter of positive column cross section which comprises mounting thesaid cathode in the envelope, charging the envelope with neon and a gasselected fronnthe group consisting of argon, krypton and xenon, theproportion of said gas being the maximum that can be employed withrespect to the current density without impairing the characteristiccolor of the neon, the range of this proportion being from 0.10 to1.50-per cent, heating the thermionic cathode to an emissivetemperatureand discharging through the positive column a current having a minimumdensity which is within the range of 0.10 to 1.0 ampere per squarecentimeter of cross section of the positive column.

' LEO L. BECK.

v being the maximum 5 that can be employed with respect to the current

